I need to compile AliRoot with the same defaults as O2 to use both at the same time, but it fails because cmake complains that alien is missing. It seems this request has been introduced in the first commit of PR #889 and it is enough to comment the line 213 of FindROOT.cmake to make AliRoot compile again. (This line issue a FATAL if alien is missing).
Is there a particular reason to enforce AliRoot to be compiled with alien? Otherwise, would it be possible to remove the request for alien in FindROOT.cmake?
I do not have an answer for your question (@dberzano might have better insight) but I would be interested in knowing what is your use case to use AliRoot and O2 together as we recently had discussions about this in a different forum.
I want to compare the tracking I am implementing in O2 with the one currently in use in AliRoot. For that I need 2 things:
convert the ESD clusters and tracks in O2 format and write them in a binary file to be used later as input for O2 tracking, so I keep O2 totally independent of AliRoot.
refit the ESD tracks with AliRoot and the O2 magnetic field so that the tracks fitted with AliRoot and O2 are strictly comparable (the 2 fields are not strictly identical probably because of different rounding in AliRoot and O2 codes).
This is done with a simple macro but it needs both AliRoot and O2 libraries at the same time to run.